The disclosures of Japanese Patent Applications No. 2000-055558 filed on Mar. 1, 2000 and No. 2001-001553 filed on Jan. 9, 2001 each including the specification, drawings and abstract are incorporated by reference in its entirety.
1. Field of the Invention
The invention relates to a valve timing control apparatus and method of an internal combustion engine.
2. Description of Related Art
Conventional internal combustion engines, such as engines installed on vehicles, are provided with a valve timing apparatus that controls the valve timing of the engine in an attempt to improve the output performance and enhance the emission quality, for example. Such a valve timing control apparatus includes a variable valve timing mechanism that is actuated by hydraulic pressure to change the valve timing of the engine. The variable valve timing mechanism includes, for example, a movable member connected to an intake camshaft of the engine, and timing advance-side hydraulic chambers and timing retard-side hydraulic chambers that are provided so as to sandwich the movable member therebetween. By selectively supplying hydraulic fluid to these hydraulic chambers so as to move the movable member by hydraulic pressure, the rotational phase (or angular position) of the camshaft relative to that of the crankshaft of the engine is changed. Thus, the relative rotation phase of the camshaft is changed in this manner, so that the valve timing of the intake valves of the engine is changed.
At the time of the start of the internal combustion engine, hydraulic fluid has been discharged from the hydraulic fluid chambers. Therefore, even if the hydraulic fluid begins to be supplied to the hydraulic chambers at the same time that the engine is started, a certain period of time is required before the movable member can be moved by hydraulic pressure. During this period, therefore, the valve timing of the intake valves cannot be controlled. Furthermore, since hydraulic pressure does not act on the movable member, the relative rotational phase of the camshaft (valve timing) is brought into the most retarded state due to reaction forces resulting from the opening and closing actions of the intake valves. In order to achieve good engine performance at the start of the engine, therefore, it may be desirable to set a (limited) control range of the valve timing of the intake valves so that valve timing suitable for the start of the engine (hereinafter, referred to as xe2x80x9cengine start valve timingxe2x80x9d) can be obtained when the valve timing is brought into the most retarded state.
However, if the control range of the valve timing is set so as to satisfy the aforementioned requirement, the control range is undesirably reduced, thus making it difficult to optimally control the valve timing over the entire operating region of the engine. In order to suppress the reduction in the control range of valve timing control while optimizing the valve timing at the time of the start of the engine, it has been proposed to fix the valve timing of the intake valves to a state in which the valve timing of the intake valves is advanced by a certain amount away from the most retarded state when the engine is started. An example of such a valve timing control apparatus that is adapted for fixing the valve timing as mentioned above is disclosed in Japanese Patent laid-open Publication (Kokai) No. 11-241608.
The apparatus disclosed in the aforementioned publication includes a spring that urges or biases a movable member so as to bring the valve timing of the intake valves to a predetermined state between the most retarded state and the most advanced state when the valve timing is currently on the retard side of the predetermined state. Then, the control range of the valve timing control is set so that the predetermined state of the valve timing becomes the engine start valve timing. Furthermore, the apparatus includes a stopper mechanism that fixes the valve timing of the intake valves when the valve timing is placed in the predetermined state (engine start valve timing) under the bias force of the spring.
In the valve timing control apparatus disclosed in the aforementioned publication, the valve timing of the intake valves is set to the engine start valve timing by the bias force of the spring at the time of the start of the engine, and the valve timing in this state is fixed by the stopper mechanism. Since the valve timing of the intake valves is fixed to the engine start valve timing upon the start of the engine in this manner, good engine performance can be achieved at the time of the start of the engine. Furthermore, when the hydraulic chambers of the variable valve timing mechanism become filled with hydraulic fluid after the engine is started, the hydraulic pressure thus developed operates to discontinue the fixed state of the valve timing established by the stopper mechanism. After the fixed state of the valve timing is discontinued, it becomes possible to optimally control the valve timing over the entire operating region of the engine by performing valve timing control over the entire control range of the valve timing control.
When the valve timing control apparatus disclosed in the aforementioned publication controls the valve timing to be the retard side of the engine start valve timing, the bias force of the spring acts on the camshaft (movable member) in the timing advancing direction. The bias force of the spring gradually increases as the relative rotational phase of the camshaft (valve timing) shifts toward the most retarded position. When the valve timing is controlled in a state in which the bias force of the spring is acting on the camshaft, the bias force, which changes with the relative rotational phase of the camshaft, adversely affects the valve timing control.
It is therefore an object of the invention to provide a valve timing control apparatus of an internal combustion engine that is capable of accurately controlling the valve timing irrespective of bias force applied by a biasing device, such as a spring, which biases the valve timing toward a predetermined state between the most retarded state and the most advanced state.
To accomplish the above and/or other objects, one aspect of the invention provides a valve timing control apparatus of an internal combustion engine that includes a biasing device that exerts a bias force so as to bring valve timing of the engine into a predetermined state when the valve timing is in a predetermined range, which control apparatus includes a controller that controls the valve timing while taking into account the bias force of the biasing device.
In the apparatus constructed as described above, even where the biasing device applies a bias force to, for example, a camshaft of intake valves, the valve timing is controlled while taking into account the bias force of the biasing device. Therefore, the valve timing can be accurately controlled irrespective of the bias force exerted by the biasing device.
In one preferred embodiment of the invention as described above, the predetermined state is between a most retarded state and a most advanced state, and the biasing device exerts the bias force so as to bring the valve timing of the engine into the predetermined state when the valve timing is on a retard side of the predetermined state. In this embodiment, the controller controls the valve timing while taking into account the bias force of the biasing device at least when the valve timing is on the retard side of the predetermined state.
With the above arrangement, while the bias force is applied by the biasing device when the valve timing is on the retard side of the predetermined state, the valve timing control is performed taking into account the biasing force, and the valve timing can be appropriately controlled regardless of the bias force.
In another preferred embodiment of the invention, the controller sets a target value of the valve timing in accordance with an operating state of the engine, and calculates a control amount used for controlling the valve timing so that the valve timing approaches the target value. The controller then calculates the control amount while taking into account the bias force of the biasing device.
Thus, the valve timing control is performed based on the control amount calculated while taking account of the bias force, and therefore the valve timing can be appropriately controlled regardless of the bias force of the biasing device.
In the above preferred embodiment, the controller may increase or decrease a control gain used for calculation of the control amount, based on an actual measurement value of the valve timing and said target value, so that the actual measurement value approaches the target value, and may correct the control gain in accordance with the bias force of the biasing device. Then, the controller may calculate the control amount used for controlling the valve timing.
As described above, the control amount used for valve timing control is calculated based on the control gain so that the actual measurement value of the valve timing approaches the target value. In this connection, the characteristic of the rate of change of the valve timing during the valve timing control differs between when the valve timing is in a range in which the bias force is applied and when the valve timing is in a range in which the bias force is not applied. If the valve timing changes from the region in which the bias force is not applied by the biasing device to the region in which the bias force is applied, for example, the characteristic of the rate of change of the valve timing becomes inappropriate, and the valve timing cannot be appropriately controlled. With the arrangement as described above, however, the control gain that is related to the characteristic of the rate of change of the valve timing is corrected in accordance with the bias force of the biasing device, and the control amount is calculated based on the control gain thus corrected, so that the valve timing can be appropriately controlled with the characteristic of the rate of change being maintained properly, regardless of the bias force of the biasing force.
In the preferred embodiment as described above, the controller may correct the control gain in accordance with the bias force of the biasing device only when the valve timing is in a range in which the biasing device exerts the bias force. With this arrangement, it may be possible to prevent the control gain from being unnecessarily corrected in accordance with the bias force when no bias force is applied by the biasing device.
Furthermore, the controller as indicated may calculate a correction value used for correction of the control gain in accordance with the bias force of the biasing device, by using the valve timing at the time of calculation.
The bias force exerted by the biasing device increases as the current valve timing shifts toward or approaches the most retarded state. If the correction value calculated in accordance with the current valve timing (i.e., the valve timing at the time of calculation) is used for calculation of the control gain as described above, it may be possible to maintain the characteristic of the rate of change of the valve timing in an appropriate state, by controlling the valve timing based on the control amount calculated from the control gain, even if the bias force of the biasing device changes with a change in the valve timing.
Preferably, the controller changes the control gain based on at least one parameter that influences the rate of change of the valve timing, in addition to the bias force of the biasing device.
When the valve timing is controlled to the target valve, a parameter or parameters that affects the rate of change of the valve timing, in addition to the bias force of the biasing device, may be changed. With the above arrangement, however, the control amount is calculated from the control gain that is changed based on the parameter(s), and the valve timing is controlled based on the control amount thus calculated, whereby the characteristic of the rate of change of the valve timing can be maintained in an appropriate state.
The controller as indicated above may control a variable valve timing mechanism based on the control amount, which variable valve timing mechanism is actuated by a pressure of hydraulic fluid so as to change the valve timing. In this case, the above-indicated at least one parameter based on which the controller changes the control gain may include one or more parameters that are related to a state of the hydraulic fluid.
With the above arrangement, the control amount is calculated from the control gain that is changed depending upon the parameter(s), and the valve timing is controlled based on the control amount thus calculated. Thus, even if the parameter(s) related to the state of the hydraulic fluid used for actuating the variable valve timing mechanism is/are changed, the characteristic of the rate of change of the valve timing can be maintained in an appropriate state.
In a still another preferred embodiment of the invention, the controller executes most retarded state learning to obtain a learned value that indicates a deviation of an actual measurement value of the valve timing when the valve timing is controlled to the most retarded state from a predetermined reference value, and calculates the control amount used for controlling the valve timing, based on the learned value. Here, the controller controls execution of the most retarded state learning while taking into account the bias force of the biasing device.
The control amount is normally calculated by using a learned value obtained by executing the most retarded state learning procedure, and the valve timing is controlled based on the control amount thus calculated, thereby reducing errors in the valve timing control due to differences among individual products, for example. However, the bias force is exerted by the biasing device when the valve timing is controlled to the most retarded position so as to implement the most retarded state learning procedure, which may result in erroneous learning of the most retarded state due to the influence of the bias force. This may make it difficult to appropriately control the valve timing. With the arrangement as described above, execution of the most retarded state learning is controlled while taking account of the bias force of the biasing device. When there is a possibility of erroneous learning of the most retarded state due to the influence of the bias force, therefore, the most retarded state learning procedure can be inhibited. By controlling execution of the most retarded state learning in this manner, the control amount (learned value) can be set to a value that accounts for the influence of the bias force, and the valve timing can be appropriately controlled without suffering from erroneous learning of the most retarded state of the valve timing.
In the above-described preferred embodiment, the biasing device may exert the bias force so as to advance the valve timing of the engine, and the controller may inhibit the most retarded state learning when an engine condition does not permit the valve timing to be controlled to the most retarded state against the bias force of the biasing device. This arrangement can avoid erroneous learning of the most retarded state of the valve timing, which may make it difficult to appropriately control the valve timing.
In the above preferred embodiment, the controller may control a variable valve timing mechanism based on the control amount, which variable valve timing mechanism is actuated by a pressure of hydraulic fluid so as to change the valve timing, and the controller may inhibit the most retarded learning when the hydraulic fluid used for actuating the variable valve timing mechanism is in a condition that does not permit the valve timing to be controlled to the most retarded state against the bias force of the biasing device. This arrangement can also avoid erroneous learning of the most retarded state of the valve timing, which may make it difficult to appropriately control the valve timing.
The valve timing control apparatus as described above may further include a memory that stores, as holding data, the control amount measured when a deviation of an actual measurement value of the valve timing from the target value thereof is maintained less than a predetermined value. In this apparatus, the controller corrects the holding data in accordance with the bias force of the biasing device, and calculates the control amount using the holding data.
The control amount used for valve timing control is calculated, using the holding data, so that the actual measurement value of the valve timing approaches the target value. The holding data provides a center with respect to which the control amount is increased or decreased. Also, the holding data is subjected to the influence of the bias force when the valve timing is in a region in which the bias force is applied by the biasing device, and is not subjected to the influence of the bias force when the valve timing is not in the same region. If the valve timing changes from a region in which the bias force is not applied by the biasing force to a region in which the bias force is applied by the biasing force, for example, the center with respect to which the control amount increases or decreases may deviate from an appropriate state or value since the holding data does not account for the influence of the bias force. Consequently, the valve timing may not be appropriately controlled. With the above arrangement of the invention, however, the control amount is calculated based on the holding data that is corrected in accordance with the bias force of the biasing device, and therefore the valve timing can be appropriately controlled without suffering from the deviation of the center of the increase/decrease of the control amount from its appropriate state.
In the above-described control apparatus, the controller may correct the holding data in accordance with the bias force only when the valve timing is in a range in which the biasing device exerts the bias force. With this arrangement, it may be possible to prevent the holding data from being unnecessarily corrected in accordance with the bias force when no bias force is applied by the biasing device.
Furthermore, the controller may correct the holding data so as to remove an influence of the bias force of the biasing device therefrom before the holding data derived from the measured control amount is stored into the memory, and may correct the holding data stored in the memory so as to add an influence of the bias force of the biasing device thereto before the holding data stored in the memory is used for calculation of the control amount.
With the above arrangement, the memory stores holding data that is free from the influence of the bias force exerted by the biasing device, and the influence of the bias force is added to the holding data when the control amount is calculated based on the holding data. Accordingly, the center with respect to which the control amount is increased or decreased can be maintained in an appropriate state even when, for example, the holding data is stored into the memory while the valve timing is in a region in which the bias force is not applied by the biasing device, and the holding data thus stored is used for calculation of the control amount when the valve timing is in a region in which the bias force is applied by the biasing device. Similarly, the center of the increase/decrease of the control amount can also be maintained in an appropriate state in the case where the holding data obtained in a region in which the biasing force is applied is stored into the memory, and the holding data thus stored is used for calculation of the control amount in a region in which the bias force is not applied.
Alternatively, the controller may inhibit the holding data from being stored into the memory when the valve timing is in a range in which the biasing device exerts the bias force, and correct the holding data stored in the memory so as to add an influence of the bias force of the biasing device thereto before the holding data stored in the memory is used for calculation of the control amount.
With the above arrangement, the memory stores holding data that is free from the influence of the bias force by the biasing device, and the influence of the bias force is added to the holding data as needed when the control amount is calculated based on the holding data. Accordingly, the center about which the control amount is increased or decreased can be maintained in an appropriate state even in the case where the holding data stored in the memory is used for calculation of the control amount when the valve timing is in a region in which the bias force is applied by the biasing device.
Alternatively, the controller may set the target value of the valve timing to a value that is outside a range in which the biasing device exerts the bias force, correct the holding data in accordance with the bias force of the biasing device, and calculate the control amount using the holding data.
With the above arrangement, the memory stores holding data that is free from the influence of the bias force by the biasing force, and the influence of the bias force is added to the holding data as needed when the control amount is calculated based on the holding data. Accordingly, the center about which the control amount is increased or decreased can be maintained in an appropriate state even in the case where the holding data stored in the memory is used for calculation of the control amount when the valve timing is in a region in which the bias force is applied.
Furthermore, the controller as indicated above may calculate a correction value used for correction of the holding data in accordance with the bias force of the biasing device, by using the valve timing at the time of calculation.
The bias force exerted by the biasing device increases as the current valve timing shifts toward or approaches the most retarded state. With the above arrangement, the holding data is corrected by using the correction value that is calculated based on the current valve timing (i.e., the valve timing at the time of calculation), and therefore the center with respect to which the control amount is increased or decreased, which is obtained from the holding data, can be maintained in an appropriate state even if the bias force of the biasing device changes with a change in the valve timing.
In a still another preferred embodiment of the invention, the valve timing control apparatus further includes a first memory that stores the control amount as first holding data at the time when a deviation of an actual measurement value of the valve timing from the target value thereof is maintained less than a predetermined value, under a condition that the valve timing is in a first range in which the biasing device exerts the bias force, and a second memory that stores the control amount as second holding data at the time when the deviation of the actual measurement value of the valve timing from the target value thereof is maintained less than the predetermined value, under a condition that the valve timing is in a second range in which the biasing device does not exert the bias force. In this embodiment, the controller calculates the control amount using the first holding data stored in the first memory when the valve timing is in the first range in which the biasing device exerts the bias force, and calculates the control amount using the second holding data stored in the second memory when the valve timing is in the second range in which the biasing device does not exert the bias force.
The control amount used for valve timing control is calculated, using the holding data, so that the actual measurement value of the valve timing approaches the target value. The holding data provides a center (or a reference value) with respect to which the control amount is increased or decreased. Also, the holding data is subjected to the influence of the bias force when the valve timing is in a region in which the bias force is applied by the biasing device, and is not subjected to the influence of the bias force when the valve timing is not in the same region. If the valve timing changes from a region in which the bias force is not applied by the biasing force to a region in which the bias force is applied by the biasing force, for example, the center with respect to which the control amount increases or decreases may deviate from an appropriate state or value since the holding data does not account for the influence of the bias force. Consequently, the valve timing may not be appropriately controlled. With the above arrangement of the invention, when the valve timing is in a region in which the bias force is applied by the biasing force, the holding data that accounts for the bias force is stored in the first memory, and the control amount used for valve timing control is calculated by using the holding data. When the valve timing is not in the above-mentioned region, on the other hand, the holding data that is free from the influence of the bias force is stored into the second memory, and the control amount is calculated by using the holding data. Thus, the storage of the holding data and the calculation of the control amount are performed separately when the valve timing is in a region in which the bias force is applied by the biasing device, and when the valve timing is not in the same region. Thus, the holding data used for calculation of the control amount can be set to a value that accounts for the bias force of the biasing device without suffering from the deviation of the center of the increase/decrease of the control amount from its appropriate state.
Preferably, the controller changes the holding data based on at least one parameter that influences the holding data, in addition to the bias force of the biasing device. With this arrangement, the control amount is calculated by using the holding data that is changed depending upon the parameter(s). Thus, the center about which the control amount is increased or decreased so as to control the valve timing to the target value can be maintained in an appropriate state even if the parameter(s) that influences the holding data, in addition to the bias force of the biasing device, changes.
In the control apparatus as described just above, the controller may control a variable valve timing mechanism based on the control amount, which to mechanism is actuated by a pressure of hydraulic fluid so as to change the valve timing, and the above-indicated at least one parameter based on which the controller changes the holding data may include one or more parameters that are related to a state of the hydraulic fluid.
With the above arrangement, the control amount is calculated from the holding data that is changed depending upon the parameter(s), and the valve timing is controlled based on the control amount thus calculated. Thus, the center about which the control amount is increased or decreased during control of the valve timing to the target value can be maintained in an appropriate state even if the parameter(s) related to the state of the hydraulic fluid for actuating the variable valve timing mechanism is/are changed.